1. Field of the Invention
This invention relates to systems and processes for continuously casting metallic materials such as steel. More specifically, this invention relates to a system and process for improving the continuous casting process by removing and/or recycling mold flux during operation.
2. Description of the Related Technology
In a conventional continuous-casting machine, liquid metal is continuously introduced into the upper end of an open-ended, water cooled, vertically oscillating mold. A casting or strand, which at this stage has only a thin solidified outer skin and a liquid core, emerges continuously from the lower end of the mold.
Typically, a powdered flux is added to the upper end of the mold in small, carefully regulated quantities of approximately one pound of flux per ton of steel that is being casted. The flux melts and covers the surface of the pool of liquid metal in the mold, and also may form a protective and lubricating layer between the solidifying skin of the casting and the mold wall. This flux, which is commonly termed "mold flux" or "mold powder" in the industry, is in effect a synthetic slag which floats on top of the molten metal, melts, works its way down in between the newly formed shell of the strand and the mold walls, and is drawn out the bottom of the mold with the cast product. It functions to thermally insulate the top surface of the molten metal, isolate the molten metal from atmospheric gases, absorb and dissolve nonmetallic inclusions that have floated up to the molten metal surface, lubricate the mold/strand interface surfaces and provide a controlled conductive transfer of heat from the strand to the mold.
Unfortunately, crystallized flux can be rolled into the surface of the cast product, severely downgrading the surface quality and contributing to downstream conditioning such as scarfing which is very costly to the steel producer. Some machine builders deliberately avoid using rollers directly below the mold for that reason, and instead use cast iron grid systems which can accelerate washing the crystallized flux away before the product reaches the first roller below that grid system. Using grids in turn drives up the operating cost of the machine through more frequent equipment changes because of the shorter life of the grid system as compared to that of a roller system.
Steam which is created immediately below the mold can be very corrosive due to reaction with various elements in the mold flux which can form hydrofluoric, carbonic, or other acids. The constant presence of these acids in the machine spray chamber can decrease the life expectancy of the machine through deterioration of such components as rolls, bearing housings, frame members, and even the main frame and support structures themselves. In severe cases it has been known to attack first zone grids in a very short time causing them to erode so badly in a single day that they no longer support the strand and a breakout occurs.